The present invention relates to a laser survey instrument, whereby laser beam is irradiated from a main unit to the object reflector and the laser beam reflected by the object reflector is detected, thus detecting the object reflector and confirming irradiating position of the laser beam.
To determine a reference for height in the field of public works and construction works, a laser survey instrument is now used, which irradiates a laser beam in a horizontal plane by rotary scanning to form a reference line or a reference plane laser beam.
In recent years, visible semiconductor laser has been introduced in practical application, and a laser survey instrument using the visible semiconductor laser has also appeared, facilitating visual operation for survey. In such laser survey instrument, laser output is limited from the viewpoint to ensure safety for the operator. For this reason, in the operation or measurement requiring visual confirmation of reflection of the laser beam, operation distance is comparatively short.
To overcome this disadvantage, a new type of laser survey instrument is now used in practical application, which is based on reciprocal scanning of a laser beam, raises apparent luminance of the laser beam and ensures a longer operation distance. In order to perform reciprocal scanning within a proper range, it is necessary to identify a scanning position. For this purpose, a laser survey instrument has been proposed, which detects a laser beam reflected from an object reflector installed at an operation point and detects the position of the object reflector. Further, this laser survey instrument emits laser beam in a vertical direction in addition to the laser beam emitted in a horizontal direction and projects the position of floor surface on ceiling. The projection of the laser beam to the ceiling is used for setting-out to indicate positioning on the ceiling and the like in construction work.
In such a laser survey instrument, in order to identify the object reflector, the emitted laser beam is turned to a polarized light beam, and it is designed in such manner that the polarized light reflected from the object reflector has a direction of polarization different from that of the emitted light. In so doing, it is possible to discriminate the object reflector from other unnecessary reflectors such as glass surface, which reflects the light while maintaining the direction of polarization.
In the conventional laser survey instrument as described above, the polarized light of the reflected light beam from the object reflector can be made different from the direction of polarization of the emitted light when the object reflector is used. However, the object reflector cannot be used for the laser beam running in a vertical direction such as the one projected to the ceiling. Therefore, in case a surface irradiated by the laser beam running in a vertical direction is near the survey instrument main unit or in case the irradiated surface has high reflectivity or a reflector having high reflectivity is present, a "harmful" reflected laser beam having the same polarized light as that of the emitted laser beam enters the laser survey instrument main unit, thereby causing erroneous operation in the detection of the object reflector.